Dorchester climate

Dorchester Frost Dates and Growing Season

NOAA 1991-2020 normals for Friend 3E, 9.1 km from Dorchester, elevation 1535 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Friend 3E. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

The last spring freeze typically comes around April 26 and the first fall freeze around October 13, a growing season of about 169 days.

Median at 36°F
last May 3, first October 4
Median at 32°F
last April 26, first October 13
Median at 28°F
last April 17, first October 21

Last freeze in spring

The chance of a later freeze than the date shown. At 10 percent, one spring in ten still freezes after the date; planting after the 10 percent date for 32°F is the cautious choice.

Threshold10%20%30%40%50%60%70%80%90%
36°FMay 14May 10May 7May 5May 3May 2Apr 30Apr 27Apr 23
32°FMay 6May 3May 1Apr 29Apr 26Apr 23Apr 20Apr 17Apr 12
28°FApr 29Apr 25Apr 22Apr 20Apr 17Apr 14Apr 11Apr 7Apr 3
24°FApr 23Apr 19Apr 15Apr 11Apr 8Apr 4Apr 1Mar 28Mar 20
20°FApr 16Apr 9Apr 5Apr 1Mar 29Mar 25Mar 21Mar 17Mar 10
16°FApr 5Mar 31Mar 26Mar 22Mar 17Mar 14Mar 10Mar 6Mar 2

First freeze in fall

The chance of an earlier freeze than the date shown. At 10 percent, one fall in ten freezes before the date.

Threshold10%20%30%40%50%60%70%80%90%
36°FSep 20Sep 25Sep 29Oct 1Oct 4Oct 6Oct 9Oct 12Oct 16
32°FSep 28Oct 2Oct 6Oct 10Oct 13Oct 15Oct 18Oct 21Oct 24
28°FOct 5Oct 12Oct 15Oct 19Oct 21Oct 24Oct 26Oct 29Nov 1
24°FOct 17Oct 22Oct 25Oct 28Oct 31Nov 2Nov 5Nov 8Nov 14
20°FOct 25Oct 31Nov 2Nov 5Nov 8Nov 11Nov 14Nov 18Nov 23
16°FNov 1Nov 6Nov 9Nov 12Nov 16Nov 20Nov 23Nov 27Dec 1

Growing season length

Days between the last spring and first fall freeze at each threshold, with the chance of a season at least that long.

Threshold10%20%30%40%50%60%70%80%90%
36°F169163159156152149145141135
32°F187181177173169166163157150
28°F205199194190186182178173166
24°F227220214210205201197192186
20°F247239234229225220215209201
16°F266259252247242237231225216

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder
100% of years
32°F or colder
100% of years
28°F or colder
100% of years
24°F or colder
100% of years
20°F or colder
100% of years
16°F or colder
100% of years

Degree days

A degree day is one degree of the daily mean temperature beyond a base, for one day. Heating degree days count cold (the fuel a house burns), cooling degree days heat, growing degree days the warmth a crop needs; each crop has its own base.

Heating degree days, base 65°F
6,426
Cooling degree days, base 65°F
873
Growing degree days, base 40°F
5,316
Growing degree days, base 45°F
4,176
Growing degree days, base 50°F
3,163
Growing degree days, base 55°F
2,272
Growing degree days, base 60°F
1,511

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,30700
February1,06203
March828130
April4835108
May19363354
June16192625
July4281742
August9225680
September10695442
October41211160
November812018
December1,19301

What this means

NOAA computes these from the daily lows at the station over 1991-2020, fitting the dates of each year's last and first freeze to a distribution, so a date can be stated at any level of risk. 36°F is a frost risk for tender plants on a clear, calm night, since the ground cools below the air above it; 32°F is a freeze; 28°F is a hard freeze that kills most annuals.

The station is 9.1 km from Dorchester. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00253065 (Friend 3E). Public domain.